Cost of gas = Distance traveled (in miles) * Fuel efficiency (in miles per gallon) * Cost of gas per gallon
Assuming a fuel efficiency of 25 miles per gallon, the cost of gas for a 1000-mile trip would be:
Cost of gas = 1000 miles * 25 MPG * $5 per gallon = $200
Therefore, the cost of gas for a 1000-mile trip at 5 dollars per gallon would be $200.